scholarly journals A Spectroscopic Study of Barium Stars

2008 ◽  
Vol 4 (S252) ◽  
pp. 425-426
Author(s):  
G. Q. Liu ◽  
Y. C. Liang ◽  
L. Deng
Keyword(s):  
Neutron Capture ◽  
Binary Systems ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Agb Stars ◽  
Atmospheric Parameters ◽  
Chemical Abundances ◽  
Capture Process ◽  
Abundance Patterns ◽  
Process Elements

AbstractWe present an analysis of eight barium stars, providing their atmospheric parameters (Teff, log g, [Fe/H], ξt) and chemical abundances, based on the high signal-to-noise ratio and high resolution Echelle spectra. The s-process elements Y, Zr, Ba, La, Eu show obvious overabundance relative to the Sun. And Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Ni show comparable abundances to the Solar ones. The results of theoretical model of wind accretion for binary systems can explain the observed abundance patterns of the neutron capture process elements in these Ba stars, which means that their overabundant heavy-elements could be caused by accreting the ejecta of AGB stars, the progenitors of the present white dwarf companions in the binary systems.

scholarly journals Abundance analysis of barium stars

2013 ◽  
Vol 9 (S298) ◽  
pp. 451-451
Author(s):  
Guochao Yang ◽  
Yanchun Liang ◽  
Wenyuan Cui ◽  
Bo Zhang
Keyword(s):  
High Resolution ◽  
Stellar Wind ◽  
Neutron Capture ◽  
White Dwarfs ◽  
Chemical Abundances ◽  
Abundance Pattern ◽  
Capture Process ◽  
Process Elements

AbstractWe obtained the chemical abundances of more than 20 Barium (Ba) stars by analysing high resolution echelle spectra. They show obvious overabundances of neutron capture process elements, such as Y, Zr, Ba, La and Eu. Their abundance pattern can be explained by binary accretion through stellar wind, where the Ba stars have accreted the ejecta from the companion stars which were in AGB stages at that time and now evolve as white dwarfs.

scholarly journals Constraining nucleosynthesis in two CEMP progenitors using fluorine

2020 ◽  
Vol 498 (3) ◽  
pp. 3549-3559
Author(s):  
Aldo Mura-Guzmán ◽  
D Yong ◽  
C Abate ◽  
A Karakas ◽  
C Kobayashi ◽  
...  
Keyword(s):  
Neutron Capture ◽  
Slow Neutron ◽  
Asymptotic Giant Branch ◽  
Capture Process ◽  
Upper Limit ◽  
Infrared Spectrometer ◽  
Binary Evolution ◽  
Vibration Rotation ◽  
R Process ◽  
Process Elements

ABSTRACT We present new fluorine abundance estimations in two carbon enhanced metal-poor (CEMP) stars, HE 1429−0551 and HE 1305+0007. HE 1429−0551 is also enriched in slow neutron-capture process (s-process) elements, a CEMP-s, and HE 1305+0007 is enhanced in both, slow and rapid neutron-capture process elements, a CEMP-s/r. The F abundances estimates are derived from the vibration–rotation transition of the HF molecule at 23358.6 Å  using high-resolution infrared spectra obtained with the Immersion Grating Infrared Spectrometer (IGRINS) at the 4-m class Lowell Discovery Telescope. Our results include an F abundance measurement in HE 1429−0551 of A(F) = +3.93 ([F/Fe] = +1.90) at [Fe/H] = −2.53, and an F upper limit in HE 1305+0007 of A(F) < +3.28 ([F/Fe] < +1.00) at [Fe/H] = −2.28. Our new derived F abundance in HE 1429−0551 makes this object the most metal-poor star where F has been detected. We carefully compare these results with literature values and state-of-the-art CEMP-s model predictions including detailed asymptotic giant branch (AGB) nucleosynthesis and binary evolution. The modelled fluorine abundance for HE 1429−0551 is within reasonable agreement with our observed abundance, although is slightly higher than our observed value. For HE 1429−0551, our findings support the scenario via mass transfer by a primary companion during its thermally pulsing phase. Our estimated upper limit in HE 1305+0007, along with data from the literature, shows large discrepancies compared with AGB models. The discrepancy is principally due to the simultaneous s- and r-process element enhancements which the model struggles to reproduce.

scholarly journals Discovery of technetium- and niobium-rich S stars: The case for bitrinsic stars

2020 ◽  
Vol 635 ◽  
pp. L6 ◽  
Author(s):  
S. Shetye ◽  
S. Van Eck ◽  
S. Goriely ◽  
L. Siess ◽  
A. Jorissen ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Chemical Abundances ◽  
Trace Evidence ◽  
Distinctive Features ◽  
The Third ◽  
Process Pattern ◽  
Process Elements ◽  
Hr Diagram

Context. S stars are late-type giants with overabundances of s-process elements. They come in two flavors depending on the presence or lack of presence of technetium (Tc), an element without stable isotopes. Intrinsic S stars are Tc-rich and genuine asymptotic giant branch (AGB) stars, while extrinsic S stars owe their s-process over abundances to the pollution from a former AGB companion, which is now a white dwarf (WD). In addition to Tc, another distinctive feature between intrinsic and extrinsic S stars is the overabundance of niobium (Nb) in the latter class. Indeed, since the mass transfer occurred long ago, 93Zr had time to decay into the only stable isotope of Nb, 93Nb, causing its overabundance. Aims. We discuss the case of the S stars BD+79°156 and o1 Ori, whose specificity lies in sharing the distinctive features of both intrinsic and extrinsic S stars, namely the presence of Tc along with a Nb overabundance. Methods. We used high-resolution HERMES optical spectra, MARCS model atmospheres of S stars, Gaia DR2 parallaxes, and STAREVOL evolutionary tracks to determine the stellar parameters and chemical abundances of the two S stars, and to locate them in the Hertzsprung-Russell (HR) diagram. Results. BD+79°156 is the first clear case of a bitrinsic star, that is, a doubly s-process-enriched object, first through mass transfer in a binary system and then through internal nucleosynthesis that is responsible for the Tc-enrichment in BD+79°156, which must, therefore, have reached the AGB phase of its evolution. This hybrid nature of the s-process pattern in BD+79°156 is supported by its binary nature and its location in the HR diagram that is just beyond the onset of the third dredge-up on the AGB. The Tc-rich, binary S-star o1 Ori with a WD companion was another long-standing candidate for a similar hybrid s-process enrichment. However, the marginal overabundance of Nb derived in o1 Ori does not allow one to trace evidence of large amounts of pollution coming from the AGB progenitor of its current WD companion unambiguously. As a side product, the current study offers a new way of detecting binary AGB stars with WD companions by identifying their Tc-rich nature along with a Nb overabundance.

scholarly journals The Chemical Composition of Post AGB Stars

1993 ◽  
Vol 155 ◽  
pp. 352-352
Author(s):  
M. Parthasarathy ◽  
P. Garcia Lario ◽  
S.R. Pottasch
Keyword(s):  
Chemical Composition ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Agb Stars ◽  
Dust Shell ◽  
Signal To Noise ◽  
Iras Source ◽  
Triple Alpha ◽  
Cno Abundances ◽  
Cold Dust

The F-type supergiant HD 56126 (F5I) is an IRAS source with detached cold dust shell with characteristics similar to the dust shells around planetary nebulae. From an analysis of high resolution and high signal to noise ratio spectra metal and CNO abundances have been determined. It is found that in HD 56126 [C/H] =−0.01, [N/H]=+0.17, [O/H] = −0.02, [S/H]=+0.01 and [Fe/H]< −1.0. The C/N/O abundance ratios and CNO abundances relative to Fe of HD 56126 and related post AGB stars suggest that they have on their photospheres the material processed by triple alpha, CN and ON cycles.

scholarly journals Study of the Abundance Patterns in the Metal-Poor Stellar Stream

2013 ◽  
Vol 30 ◽  
Author(s):  
Hongjie Li ◽  
Shuai Liang ◽  
Wenyuan Cui ◽  
Bo Zhang
Keyword(s):  
Gradual Increase ◽  
Type Ii ◽  
Constant Mass ◽  
Chemical Abundances ◽  
Abundance Patterns ◽  
The Difference ◽  
The Masses ◽  
Process Component ◽  
Process Elements ◽  
Early Galaxy

AbstractThe chemical abundances of the metal-poor stars in the stellar stream provide important information for setting constraints on models of neutron-capture processes. The study of these stars could gives us a better understanding of the r-process nucleosynthesis and chemical composition of the early Galaxy. Using the updated main r-process and weak r-process patterns, we fit abundances in the stellar stream stars. The weak r-process component coefficients are almost constant for the sample stars, including r-rich stars, which means that both the weak r-process and Fe are produced as primary elements from Type II supernovae and their yields have nearly a constant mass fraction. The difference between the stream stars and r-rich stars is obvious. For the stream stars, the fact that the increased trend in the main r-process component coefficients as metallicity increases means a gradual increase in the production of main r-process elements relative to iron. This behaviour implies that the masses of progenitors for the main r-process are smaller than those of the weak r-process. Furthermore, we find that the metal-poor stream star HD 237846 is a weak r-process star.

The RAdial Velocity Experiment: preparing the 6th Data Release chemical abundances with GAUGUIN

2017 ◽  
Vol 13 (S334) ◽  
pp. 302-303
Author(s):  
Guillaume Guiglion ◽  
Keyword(s):  
Radial Velocity ◽  
Milky Way ◽  
Chemical Elements ◽  
Elemental Abundance ◽  
Atmospheric Parameters ◽  
Chemical Abundances ◽  
Abundance Patterns ◽  
Medium Resolution ◽  
Data Release ◽  
Future Data

AbstractIn the context of the Radial Velocity Experiment (RAVE, Steinmetz et al. 2006), we present chemical abundances derived with the pipeline GAUGUIN. Based of 520 701 RAVE stars with medium resolution (R~7 500) spectra and stellar atmospheric parameters of the fifth Data Release, the analysis is performed around the infrared Ca-triple domain for 6 chemical elements: Mg, Ni, Si, Ti, Fe and Al. We discuss here the reliability of the chemical abundances provided by GAUGUIN, and the implications for the future Data Release 6 of the RAVE Survey. We also present elemental abundance patterns of Milky Way components based of kinematical criteria.

The role of AGB stars in Galactic and cosmic chemical enrichment

2018 ◽  
Vol 14 (S343) ◽  
pp. 247-257
Author(s):  
Chiaki Kobayashi ◽  
Christopher J. Haynes ◽  
Fiorenzo Vincenzo
Keyword(s):  
Electron Capture ◽  
Galaxy Formation ◽  
Neutron Capture ◽  
Slow Neutron ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Capture Process ◽  
Chemical Enrichment ◽  
Cno Abundances

AbstractThe role of asymptotic giant branch (AGB) stars in chemical enrichment is significant for producing 12,13C, 14N, F, 25,26Mg, 17O and slow neutron-capture process (s-process) elements. The contribution from super-AGB stars is negligible in classical, one-zone chemical evolution models, but the mass ranges can be constrained through the contribution from electron-capture supernovae and possibly hybrid C+O+Ne white dwarfs, if they explode as Type Iax supernovae. In addition to the recent s-process yields of AGB stars, we include various sites for rapid neutron-capture processes (r-processes) in our chemodynamical simulations of a Milky Way type galaxy. We find that neither electron-capture supernovae or neutrino-driven winds are able to adequately produce heavy neutron-capture elements such as Eu in quantities to match observations. Both neutron-star mergers (NSMs) and magneto-rotational supernovae (MRSNe) are able to produce these elements in sufficient quantities. Using the distribution in [Eu/(Fe, α)] – [Fe/H], we predict that NSMs alone are unable to explain the observed Eu abundances, but may be able to together with MRSNe. In order to discuss the role of long-lifetime sources such as NSMs and AGB stars at the early stages of galaxy formation, it is necessary to use a model that can treat inhomogeneous chemical enrichment, such as in our chemodynamical simulations. In our cosmological, chemodynamical simulations, we succeed in reproducing the observed N/O-O/H relations both for global properties of galaxies and for local inter-stellar medium within galaxies, without rotation of stars. We also predict the evolution of CNO abundances of disk galaxies, from which it will be possible to constrain the star formation histories.

Nucleosynthesis in stars: The Origin of the Heaviest Elements

2018 ◽  
Vol 14 (S343) ◽  
pp. 79-88 ◽  
Author(s):  
Amanda I. Karakas
Keyword(s):  
Chemical Evolution ◽  
Neutron Capture ◽  
Recent Progress ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Capture Process ◽  
Intermediate Mass Stars ◽  
Intermediate Neutron ◽  
Heaviest Elements ◽  
The Universe

AbstractThe chemical evolution of the Universe is governed by the nucleosynthesis contribution from stars, which in turn is determined primarily by the initial stellar mass. The heaviest elements are primarily produced through neutron capture nucleosynthesis. Two main neutron capture processes identified are the slow and rapid neutron capture processes (s and r processes, respectively). The sites of the r and s-process are discussed, along with recent progress and their associated uncertainties. This review is mostly focused on the s-process which occurs in low and intermediate-mass stars which have masses up to about 8 solar masses (M⊙). We also discuss the intermediate-neutron capture process (or i-process), which may occur in AGB stars, accreting white dwarfs, and massive stars. The contribution of the i-process to the chemical evolution of elements in galaxies is as yet uncertain.

scholarly journals Heavy elements in planetary nebulae: A theorist's gold mine

2011 ◽  
Vol 7 (S283) ◽  
pp. 127-130
Author(s):  
Amanda I. Karakas ◽  
Maria Lugaro
Keyword(s):  
Neutron Capture ◽  
Planetary Nebulae ◽  
Asymptotic Giant Branch ◽  
Heavy Elements ◽  
Gold Mine ◽  
Agb Stars ◽  
Capture Process ◽  
Wide Range ◽  
Model Predictions

AbstractObservations of planetary nebulae have revealed a wealth of information about the composition of heavy elements synthesized by the slow neutron capture process (the s process). In some of these nebulae the abundances of neutron-capture elements are enriched by factors of 10 to 30 times the solar value, indicating that these elements were produced in the progenitor star while it was on the asymptotic giant branch (AGB). In this proceedings we summarize results of our recent full s-process network predictions covering a wide range of progenitor masses and metallicities. We compare our model predictions to observations and show how this can provide important insights into nucleosynthesis processes occurring deep within AGB stars.

scholarly journals Comparison of errors between a differential and a classical abundance analysis

2017 ◽  
Vol 95 (9) ◽  
pp. 855-857
Author(s):  
Henrique Reggiani ◽  
Jorge Meléndez
Keyword(s):  
Measurement Errors ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Differential Analysis ◽  
Analysis Method ◽  
Chemical Abundances ◽  
Differential Abundance ◽  
Low Metallicity ◽  
Low Levels ◽  
Differential Abundance Analysis

The differential abundance analysis method can improve the precision of stellar chemical abundances. The method compares the equivalent widths of a certain line in a star with the same line in a star considered to be a standard representative of its class, using high resolution and high signal to noise ratio spectra. The method has achieved great results by reducing the measurement errors to unprecedentedly low levels. However, to date, there has not been a consistent analysis on the actual improvements of this method when compared to a classical analysis in metal-poor stars. Here we present a comparison between the errors of a classical stellar analysis and a differential analysis among low-metallicity stars.

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